A hallmark of atopic allergy is the formation of IgE antibodies to proteins present in the sensitizing biological material. Upon contact with the allergen source, these proteins will act to crosslink IgE antibodies present on the surface of mast cells, thereby eliciting the release of inflammation mediators such as histamine. As a result, an allergic reaction occurs (1).
In the industrialized world, up to 10% of the human population shows allergic sensitization to grass pollen, making this one of the most important airborne allergen sources (2). Considerable efforts have been made towards the characterization of pollen allergens from a variety of grass species using biochemical and immunological methods. A number of IgE binding proteins have thus been identified which exhibit conserved structure and serological cross-reactivity between species. Based on these criteria, such immunologically related grass pollen allergens have been assigned to groups designated by numbers. These include group 1, group 2/3, group 4, and group 5 allergens, which are represented in pollen of most grass species (3).
To date, six different allergens from timothy grass (Phleum pratense) pollen have been cloned: Phl p 1 (4, 5), Phl p 2 (6), Phl p 5 (7-9), Phl p 6 (10, 11), Phl p 7 (12), Phl p 12 (profilin) (13), and Phl p 13 (14). These allergens have all been produced as recombinant proteins which, by different in vitro and in vivo activity assays, have been shown to share immunological and allergenic properties with their native counterparts.
Using a panel of four recombinant allergens (rPhl p 1, rPhl p 2, rPhl p 5, and profilin) in serological and skin testing procedures, positive results were obtained in 95% of a large population of grass pollen-allergic individuals (15). Sensitization to allergens such as Phl p 7 (a calcium-binding, two-EF-hand protein) and Phl p 12 occurs in a smaller proportion of grass pollen allergics, but they share IgE epitopes with homologous proteins present in pollen of trees and weeds and can therefore cause immediate-type symptoms in sensitized individuals upon contact with these unrelated allergen sources (12, 16, 17).